In the relevant literature, there are multiple ways to align fibers, especially carbon nanotubes (CNTs), such as by magnetic field (see, e.g., Tian Y. et al. Nanotechnology 20, 335601 (2009); and Steinert, B. W. et al. Polymer 50, 898 (2009)), gas flow (see, e.g., Xin H. et al. Nano Letters 4, 1481 (2004); and Hedberg, J. et al. Applied Physics Letters 86, 143111 (2005)), shear flow of polymer matrix (see, e.g., Abu Bakar S. et al. Journal of Composite Materials 45, 931 (2010)), mechanical shear press (see, e.g., Wang D. et al. Nanotechnology 19, 075609 (2008)), and mechanical stretch alignment (see, e.g., Cheng, Q. et al. Advanced Functional Materials 19, 3219 (2009)). These techniques, however, typically require high cost, are complex, and/or restrict the possible sizes of the samples containing the fibers.
For example, the use of mechanical forces to align CNTs or carbon nanofibers (CNFs) can permit the alignment of large samples, but typically requires the CNTs to have specific characteristics and/or involves a complicated process. Mechanical processing also can cause damage to the fibers' microstructure, thereby reducing mechanical strength. The use of a mechanical force also can make it difficult to realize a mat or tissue shaped fiber preform.
Also, the use of magnetic forces typically is costly and not environmentally friendly, because obtaining sufficient magnetic forces to align fibers usually requires an intense field to magnetize the fibers to micro-magnets, which consumes relatively large amounts of energy and increases processing costs.
Therefore, improved alignment methods that do not rely on magnetic and/or mechanical forces to align fibers are desirable. Also desired are alignment methods that lessen the risk of damaging the fibers, that do not consume relatively large amounts of energy, and/or that permit the alignment of fibers in relatively large samples.